Gene defect found for unexplained male infertility
Researchers may have found a clue to male infertility that could help explain why so many cases can't be explained. University of California -Davis scientists discovered a defect in the DEFB126 gene that they say is carried by a high number of men. When the gene is mutated, sperm can’t get through cervical mucus because it lacks a protein coat needed to evade the immune system.
Half of men have gene defect that affects fertility
The researchers note the importance of the finding. In their DNA sampling from the U.S., United Kingdom, China, Japan and Africa they found that half of men have at least one DEFB126 gene mutation. Twenty five percent of men were found to have two defective copies of the gene that they say significantly affects male fertility.
The gene acts like a cloaking device, providing sperm with a necessary protein that has nothing to do with sperm quality and quantity. Even when sperm looks good under the microscope, it can’t get to the egg without the protein coat.
Gary Cherr, a professor at the UC Davis Bodega Marine Laboratory and Center for Health and Environment and senior author of the paper explains, "In 70 percent of men, you can't explain their infertility on the basis of sperm count and quality.”
But Cherr says sperm that are poor swimmers may serve a purpose explaining why the mutation is so common. Compared to monkeys, human male sperm is typically inferior. Cherr says it may be related to monogamy and long-term human relationships that makes sperm quality less important than in the animal kingdom.
Ted Tollner, first author of the paper says it’s been a mystery as to why sperm quality and quantity has so little to do with male fertility.
The discovery came about when Tollner and Cherr were investigating how to make contraceptive vaccines.
The researchers explain DEFB126 is made in the epididymis where sperm is stored. The gene provides a thick coating. The scientists were trying to make an antibody against the protein that belongs to a class of defensins, with little success.
They researchers consulted Professor Charles Bevins, an expert on defensins and new member of the UC Davis Department of Medical Microbiology and Immunology. Bevins cloned the gene in the hopes that the researchers could then produce the antibody from purified protein. That’s when they found the mutation. When they tried with a different donor, the researchers were successful.
Bevins said, “If we hadn't seen this in the first clone, we would be confused to this day.” When the scientists added the protein the sperms reverted to normal behavior.
The finding is significant because male infertility is also linked to a shorter lifespan.
Male fertility seems to be on the decline worldwide. The researchers say the DEFB126 gene mutation, found in a significant number of men, might explain high rates of male infertility. They also say there may be a reason the gene mutation is so prevalent. The next step is to understand why the sperm mutation is so prevalent.
Science Translational Medicine; DOI: 10.1126/scitranslmed.3002289
“A Common Mutation in the Defensin DEFB126 Causes Impaired Sperm Function and Subfertility”
Theodore L Tollner et al; July 2011
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